U.S. patent application number 12/084979 was filed with the patent office on 2009-07-02 for active cannula for bio-sensing and surgical intervention.
This patent application is currently assigned to The Johns Hopkins University. Invention is credited to Noah J. Cowan, Allison M. Okamura, Russell H. Taylor, Robert James Webster.
Application Number | 20090171271 12/084979 |
Document ID | / |
Family ID | 38049282 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090171271 |
Kind Code |
A1 |
Webster; Robert James ; et
al. |
July 2, 2009 |
Active Cannula for Bio-Sensing and Surgical Intervention
Abstract
Disclosed is a surgical needle, or active cannula, that is
capable of following a complex path through cavities and tissue
within a patient's anatomy. The needle has a plurality of
overlapping flexible tubes, each of which has a pre-formed
curvature and a pre-determined flexibility. Each of the plurality
of flexible tubes is selected based on their respective pre-formed
curvature and flexibility so that a given overlap configuration
causes the combination of overlapping flexible tubes to form a
predetermined shape that substantially matches a desired path
through the anatomy. By individually controlling the translation
and angular orientation of each of the flexible tubes, the surgical
needle may be guided through the anatomy according to the desired
path.
Inventors: |
Webster; Robert James;
(Nashville, TN) ; Okamura; Allison M.; (Ruxton,
MD) ; Cowan; Noah J.; (Baltimore, MD) ;
Taylor; Russell H.; (Severna Park, MD) |
Correspondence
Address: |
MCKENNA LONG & ALDRIDGE LLP
1900 K STREET, NW
WASHINGTON
DC
20006
US
|
Assignee: |
The Johns Hopkins
University
Baltimore
MD
|
Family ID: |
38049282 |
Appl. No.: |
12/084979 |
Filed: |
November 15, 2006 |
PCT Filed: |
November 15, 2006 |
PCT NO: |
PCT/US2006/044386 |
371 Date: |
December 11, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60736789 |
Nov 15, 2005 |
|
|
|
60849788 |
Oct 6, 2006 |
|
|
|
Current U.S.
Class: |
604/95.01 |
Current CPC
Class: |
A61B 1/0055 20130101;
A61M 2025/0161 20130101; A61M 25/0108 20130101; A61B 17/3478
20130101; A61B 2017/003 20130101; A61B 17/3417 20130101; A61M
25/0127 20130101; A61B 2017/00809 20130101; A61B 17/3421 20130101;
A61B 2017/00398 20130101; A61B 2034/301 20160201; A61B 2017/00331
20130101; A61M 25/0152 20130101 |
Class at
Publication: |
604/95.01 |
International
Class: |
A61M 5/00 20060101
A61M005/00 |
Claims
1. A surgical cannula, comprising: a first flexible tube having a
first pre-formed curvature; a second flexible tube having a second
pre-formed curvature, wherein the second flexible tube is disposed
within the first flexible tube; a first actuator coupled to the
first flexible tube, wherein the first actuator controls a
translation and a rotation of the first flexible tube; and a second
actuator coupled to the second flexible tube, wherein the second
actuator controls a rotation and translation of the second flexible
tube independently of the translation and rotation of the first
flexible tube.
2. The surgical cannula of claim 1, wherein the first flexible tube
is stiffer than the second flexible tube.
3. The surgical cannula of claim 1, wherein the first flexible tube
has a first stiffness and the second flexible tube has a second
stiffness, and wherein the first stiffness and the second stiffness
are substantially equal.
4. The surgical cannula of claim 1, wherein the first flexible tube
comprises nitinol.
5. The surgical cannula of claim 1, wherein the first flexible tube
has a straight portion.
6. The surgical cannula according to claim 1, wherein the first
flexible tube comprises a region having a complex shape.
7. The surgical cannula according to claims 1, wherein the first
flexible tube comprises a plurality of regions, wherein for each of
the plurality of regions the first flexible tube has a different
thickness.
8. The surgical cannula of claim 1, wherein the second flexible
tube comprises nitinol.
9. The surgical cannula of claim 1, wherein the second flexible
tube has a straight portion.
10. The surgical cannula according to claim 1, wherein the second
flexible tube comprises a region having a complex shape.
11. The surgical cannula according to claims 1, wherein the second
flexible tube comprises a plurality of regions, wherein for each of
the plurality of regions the second flexible tube has a different
thickness.
12. The surgical cannula of claim 1, further comprising a computer
connected to the first actuator and the second actuator, wherein
the computer comprises a computer readable medium encoded with a
program for determining a shape of the surgical cannula based on a
first flexible tube linear position; a first flexible tube angular
orientation; the first pre-formed curvature; a second flexible tube
linear position; a second flexible tube angular orientation; the
second pre-formed curvature; and an overlap between the first
flexible tube and the second flexible tube.
13. The surgical cannula of claim 1, further comprising: a third
flexible tube having a third pre-formed curvature, wherein the
third flexible tube is disposed within the second flexible tube;
and a third actuator coupled to the third flexible tube.
14. The surgical cannula of claim 13, further comprising a computer
connected to the first actuator, the second actuator, and the third
actuator, the computer having a computer readable medium encoded
with a program for determining a shape of the surgical cannula
based on the a first flexible tube linear position; a first
flexible tube angular orientation; the first pre-formed curvature;
a second flexible tube linear position; a second flexible tube
angular orientation; the second pre-formed curvature; a third
flexible tube linear position; a third flexible tube angular
orientation; the third pre-formed curvature; and an overlap between
the first flexible tube, the second flexible tube, and the third
flexible tube.
15. A computer readable medium encoded with software for guiding a
surgical cannula, the software comprising: a program that receives
a desired cannula path; a program that computes a configuration of
a plurality of overlapping flexible tubes that substantially
matches the desired cannula path; a program that computes a
plurality of intermediate configurations corresponding to the
desired cannula path; and a program that commands a plurality of
actuators according to the plurality of intermediate
configurations.
16. The computer readable medium of claim 15, wherein the software
further comprises: a program that acquires an image of the cannula;
a program that registers the cannula position within the image; and
a program that compares the cannula position to the desired cannula
path.
17. The computer readable medium of claim 16, wherein the software
further comprises a program that computes a force and a torque
applied to the cannula.
18. The computer readable medium of claim 15, wherein the program
that computes a configuration of the plurality of overlapping tubes
comprises: a program that identifies a plurality of overlapping
regions; a program that computes a curvature for each of the
plurality of overlapping regions based on a pre-formed curvature of
each of a plurality of overlapping flexible tubes within each of
the overlapping regions and a flexibility of each of the
overlapping flexible tubes.
19. A method for guiding a surgical cannula having a plurality of
overlapping flexible tubes, comprising: determining a desired
cannula path; selecting the plurality of flexible tubes, wherein
each of the flexible tubes within the plurality has a pre-formed
curvature and a flexibility; determining a final overlap
configuration of the plurality of flexible tubes such that a
resulting curvature of the overlap configuration substantially
corresponds to the desired cannula path; and determining a
plurality of intermediate overlap configurations of the plurality
of flexible tubes, wherein each of the intermediate configurations
correspond to the desired cannula path.
20. The method of claim 19, wherein the determining the final
overlap configuration comprises determining a translation and a
rotation for each of the plurality of overlapping flexible
tubes.
21. The method of claim 19, further comprising translating and
rotating each of the plurality of flexible tubes according to each
of the plurality of intermediate overlap configurations.
22. The method of claim 19, wherein the determining the final
overlap configuration comprises: selecting an initial set of
translations and rotations corresponding to each of the plurality
of overlapping flexible tubes; identifying a plurality of overlap
regions corresponding to the initial set of translations and
rotations; computing an instantaneous curvature corresponding to
each of the plurality of overlapping regions.
23. The method of claim 22, wherein computing an instantaneous
curvature corresponding to each of the plurality of overlapping
regions comprises: computing a torsional energy corresponding to a
straight section of the surgical cannula; computing a bending
energy corresponding to the surgical cannula; and solving for a
surgical cannula shape that corresponds to a minimum torsional
energy and a minimum bending energy.
Description
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/736,789, titled ACTIVE CANNULAS FOR
BIO-SENSING AND SURGICAL INTERVENTION, filed on Nov. 15, 2005, and
U.S. Provisional Patent Application No. 60/849,788, titled METHOD
FOR CONTROLLING SNAKE-LIKE ROBOTS FOR SURGICAL APPLICATIONS, filed
on Oct. 6, 2006, which are hereby incorporated by reference for all
purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to surgical cannulas
and bio-sensors for minimally invasive surgery. More particularly,
the present invention relates to devices and techniques for guiding
surgical instruments, injectable matter, diagnostic devices, and/or
bio-sensors through complex trajectories.
[0004] 2. Discussion of the Related Art
[0005] Minimally invasive surgical (MIS) techniques have
revolutionized medicine in recent years by enabling surgical
treatment without the massive trauma typically resulting from
traditional open surgery. MIS techniques have enabled physicians to
gain access to and perform interventions in anatomical regions
previously unreachable under open surgical techniques. Further, MIS
techniques have greatly reduced the trauma associated with surgery,
thereby reducing surgery-related complications and expediting
post-surgery recovery. Without viable MIS alternatives, surgery in
confined spaces within the body (especially the head and neck)
require large incisions and destructive dismantlement of healthy
bone, skin, and muscle structure simply to enable tool access to
the surgical site.
[0006] Related art MIS tools include rigid laparoscopic devices,
which require a great deal of open space both inside and outside
the body to perform dexterous motions in surgery. This requirement
for open space generally precludes the use of laparoscopic devices
in many types of surgery. Other related art MIS tools include
flexible shape memory alloy devices, in which the shape of the
device can be changed be applying heat to the shape memory alloy as
the device is guided within a patient. One problem with such a
device involves the unintended application of heat to the
surrounding tissue. Another problem is that the thermal time
constants of the shape memory alloy require considerable time (as
long as several seconds) for appropriate heat to be applied and
subsequently dissipated. The delays imposed by these thermal time
constants limit the applicability of such MIS devices.
[0007] Other related art MIS devices include teleoperated surgical
robots that typically have 5-10 mm diameter straight and rigid
tools, which have a wire-actuated or push rod-actuated wrist. A
problem with such related art surgical robots is that they are
constrained to pivot at the body entry point and do not have the
dexterity. to maneuver through curved trajectories and around
obstacles once within the body. By being constrained to pivoting at
the body entry point, such surgical robots are generally unsuitable
for complex surgical procedures, such as fetal surgery within the
womb. In the case of fetal surgery, at least two pivot points are
required: one at the mother's skin, and another at the wall of the
uterus.
[0008] Surgical interventions involving the head and neck are
particularly challenging, even with the advent of MIS techniques.
For example, treatment of lesions at the base of the skull
typically involve MIS devices being endoscopically inserted through
the nose. Because related art MIS devices lack the dexterity to
bend around and through small openings in the sinus cavities, many
healthy tissue and bone structures, such as the nasal turbinates,
must be removed to enable the MIS devices to access various
surgical sites, including the base of the skull. Regarding nasal
turbinates, their normal functions are to purify air and to aid in
olefaction. Once removed for the purposes of gaining access to
surgical sites, they cannot be reconstructed in such a way that
their function is restored. Two exemplary surgical sites that
cannot be reached using related art straight MIS devices include
areas behind the carotid arteries (near the base of the eye) and
the frontal sinus cavities, which involve reaching around a bone
located directly behind the bridge of the nose.
[0009] Other examples of a surgical procedures in which related art
MIS devices lack dexterity is lung surgery and throat surgery.
Regarding lung surgery, a related art bronchoscope generally can
only reach about 1/3 of the lung's interior. Currently, there are
no low-risk methods of removing biopsy samples or directly treating
cancer deeper within the lung. Further other related art methods of
lung biopsy and treatment involve inserting needles, which incurs a
substantial risk of complications, including lung deflation.
Regarding throat surgery, lesions located deep within the throat
are very difficult to access without large incisions. The large
incisions are typically made to enable suturing. The throat itself
as an avenue for suturing would mitigate the need for large
incisions. However, related art MIS devices lack the dexterity to
travel long distances through a laryngoscope, which typically has
an 11 mm diameter.
[0010] Accordingly, what is needed is a surgical tool that has the
dexterity to be maneuvered around anatomical features in order to
gain access to otherwise unreachable surgical sites. Further, what
is needed is a surgical device that can be guided through free
space within a cavity, such as the sinuses, throat, and lungs, as
well as through a tissue medium.
SUMMARY OF THE INVENTION
[0011] The present invention provides an active cannula for
bio-sensing and surgical intervention that obviates one or more of
the aforementioned problems due to the limitations of the related
art.
[0012] Accordingly, one advantage of the present invention is that
it provides a physician with better access to areas within the body
that are typically unreachable.
[0013] Another advantage of the present invention is that it
reduces the collateral trauma imposed on tissues in the course of
gaining access to a tissue region of interest.
[0014] Still another advantage of the present invention is that it
enables novel treatment methods.
[0015] Still another advantage of the present invention is that
increases the accessibility of anatomical features to needles for
the purposes of therapy and diagnostics.
[0016] Still another advantage of the present invention is that it
provides better maneuverability for surgical instruments through
both free space and tissue media.
[0017] Still another advantage of the present invention is that
enhances the miniaturization of surgical cannulas.
[0018] Still another advantage of the present invention is that it
enables safer guiding of surgical instruments in the presence of
sensitive tissue.
[0019] Additional advantages of the invention will be set forth in
the description that follows, and in part will be apparent from the
description, or may be learned by practice of the invention. The
advantages of the invention will be realized and attained by the
structure pointed out in the written description and claims hereof
as well as the appended drawings
[0020] To achieve these and other advantages, the present invention
involves a surgical cannula. The surgical cannula comprises a first
flexible tube having a first pre-formed curvature; a second
flexible tube having a second pre-formed curvature, wherein the
second flexible tube is disposed within the first flexible tube; a
first actuator coupled to the first flexible tube, wherein the
first actuator controls a translation and a rotation of the first
flexible tube; and a second actuator coupled to the second flexible
tube, wherein the second actuator controls a rotation and
translation of the second flexible tube independently of the
translation and rotation of the first flexible tube.
[0021] In another aspect of the present invention, the
aforementioned and other advantages are achieved by a computer
readable medium encoded with software for guiding a surgical
cannula, which comprises a program that receives a desired cannula
path; a program that computes a configuration of a plurality of
overlapping flexible tubes that substantially matches the desired
cannula path; a program that computes a plurality of intermediate
configurations corresponding to the desired cannula path; and a
program that commands a plurality of actuators according to the
plurality of intermediate configurations.
[0022] In another aspect of the present invention, the
aforementioned and other advantages are achieved by a method for
guiding a surgical cannula having a plurality of overlapping
flexible tubes. The method comprises determining a desired needle
path; selecting the plurality of flexible tubes, wherein each of
the flexible tubes within the plurality has a pre-formed curvature
and a flexibility; determining a final overlap configuration of the
plurality of flexible tubes such that a resulting curvature of the
overlap configuration substantially corresponds to the desired
needle path; and determining a plurality of intermediate overlap
configurations of the plurality of flexible tubes, wherein each of
the intermediate configurations correspond to the desired needle
path.
[0023] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention.
[0025] FIG. 1 illustrates an active cannula, and a system for
controlling it, according to the present invention;
[0026] FIG. 2A illustrates an exemplary outer tube of the active
cannula;
[0027] FIG. 2B illustrates an exemplary middle tube of the active
cannula;
[0028] FIG. 2C illustrates an exemplary inner tube of the active
cannula;
[0029] FIG. 2D illustrates an exemplary active cannula that
includes the three tubes illustrated in FIGS. 2A-C;
[0030] FIG. 3; further illustrates the active cannula of FIG. 2B,
including degrees of freedom of each tube;
[0031] FIG. 4A illustrates a set of two-axis actuators according to
the present invention;
[0032] FIG. 4B illustrates an exemplary mechanism for a two-axis
actuator;
[0033] FIG. 5 illustrates a set of manual actuators;
[0034] FIG. 6 is an exemplary process for controlling an active
cannula;
[0035] FIG. 7 illustrates a kinematic frame for controlling a tube;
and
[0036] FIG. 8 illustrates how strain relates to the side lengths
and curvature of a tube.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0037] The present invention involves an active cannula, (also
referred to as a surgical cannula) through which a surgical needle
may be deployed. The active cannula may also be referred to as a
snake-like surgical robot. The active cannula has a plurality of
concentric flexible hollow tubes, wherein each tube has a
predetermined flexibility and a pre-formed curvature. The tip of
the active cannula is advanced by selectively translating and
rotating each of the flexible tubes. Depending on the flexibility,
preformed curvature, angular orientation, and translational
position of each of the flexible tubes, the active cannula can be
manipulated to take a planned complex shape that enables it to
maneuver through free space (e.g., navigating through sinus
passages or within bronchial airways) and/or through tissues of
various resistances. The shape of the active cannula will also be
affected by the resistance of the tissue medium in such a way that
the resistance of the tissue medium may be taken advantage of in
guiding the active cannula. Continuous actuation of the active
cannula is derived from the elastic energy stored in each of the
flexible tubes as each of the flexible tubes slide within each
other during translation and rotation.
[0038] Further, the active cannula may take a complex shape as it
is guided, either through free space or through a tissue medium, by
"pushing against itself" via the interacting forces of the
concentric flexible tubes. This contrasts with related art
approaches of guiding needles by having them push against the
tissue medium, wherein the tissue medium may be a soft tissue, or
an anatomical feature such as an arterial wall.
[0039] FIG. 1 illustrates an exemplary system 100 for controlling
an active cannula according to the present invention. System 100
includes an active cannula 102 having an outer flexible tube 110, a
middle flexible tube 115, and an inner flexible tube 120. Inner
flexible tube 120 may have an end effector 125 at its end. System
100 further includes an inner drive module 140, which is coupled to
inner flexible tube 120; a middle drive module 135, which is
coupled to middle flexible tube 115; and an outer drive module 130,
which is coupled to outer flexible tube 110. Inner drive module
140, middle drive module 135, and outer drive module 130 are
connected to control computer 145.
[0040] Control computer 145 is connected to a host computer 150
over a control network connection 146a. Control network connection
146a may be a local area network (LAN) if host computer 150 and
control computer 145 are co-located. Alternatively, host computer
150 and control computer 145 may be separated by great distances,
in which case control network connection 146a may include the
internet.
[0041] Host computer 150 includes a memory 152, which is encoded
with software (hereinafter "the software") for implementing
processes associated with the present invention. Host computer 150
is connected to a user interface 155. Host computer 150 may be a
single computer or may include multiple computers that may be
connected over a network, including the internet. Memory 152 may
include a single memory device, such as a hard drive, or it may
include multiple memory devices and databases that are distributed
over multiple computers. One skilled in the art will readily
appreciate that many such architectures for host computer 150,
memory 152, and user interface 155, are possible and within the
scope of the invention.
[0042] System 100 may further include a medical imaging system 160,
which includes an image processor 165. Image processor 165 may be
connected to host computer 150 over imaging network connection
146b, which may be the same type of network connection as control
network connection 146a.
[0043] FIG. 1 illustrates active cannula 102 being deployed within
a patient's anatomy 170, both of which are within the field of view
of medical imaging system 160. Patient's anatomy 170 includes an
entry point 175, where active cannula 102 enters the patient; and
surgical site 180, which is the target site of interest within the
patient at which the surgical intervention or diagnostic is to be
performed.
[0044] Medical imaging system 160 may include one or more medical
imaging modalities, such as fluoroscopy, MRI, ultrasound, and the
like. The particular imaging modality of medical imaging system 160
may depend on the material used for active cannula 102 and the
nature of the patient's anatomy 170 in which active cannula 102 is
being deployed. Medical imaging system 160 may be of a type that
provides 3-dimensional images with sufficient timeliness and
sufficient frame rate to enable image-based feedback control of
active cannula 102 by the software running on host computer
152.
[0045] FIGS. 2A-2D illustrate active cannula 102 and its
constituent flexible tubes. FIG. 2A illustrates an exemplary outer
flexible tube 110. Outer flexible tube 110 may have an outer tube
straight section 210, an outer tube curved section 212, and an
outer tube transition point 211 defining the boundary between outer
tube straight section 210 and outer tube curved section 212. Outer
flexible tube 110 may have an inner diameter that is sufficiently
wide to allow middle flexible tube 115 and inner flexible tube 120
to slide independently within the inner surface of outer flexible
tube 110. The thickness of outer flexible tube 110 may be a
function of the tube's desired flexibility, which is described
herein further below. Accordingly, the thickness of outer flexible
tube 110 may be tailored to provide a specified flexibility. The
illustrated circular curvature of outer flexible tube 110 is
exemplary, and many different curved shapes are possible, given the
tube's material, its thickness, and the intended use of active
cannula 102.
[0046] Outer flexible tube 110 may be made of a shape memory alloy,
such as nitinol, although other materials may be used provided that
they are suitable for surgical use and have a flexibility that can
be predetermined by, for example, material properties or by
specifying the thickness of the tube walls.
[0047] FIG. 2B illustrates an exemplary middle flexible tube 115.
Middle flexible tube 115 may have a middle tube straight section
215, a middle tube curved section 217, and a middle tube transition
point 216 defining the boundary between middle tube straight
section 215 and middle tube curved section 217. Middle flexible
tube 115 may have an inner diameter that is sufficiently wide to
allow inner flexible tube 120 to slide within the inner surface of
middle flexible tube 115. The thickness of middle flexible tube 115
may be a function of the tube's desired flexibility, which is
described herein further below. Accordingly, the thickness of
middle flexible tube 115 may be tailored to provide a specified
flexibility. The illustrated curvature of middle flexible tube 115
is exemplary, and many different curvatures are possible, given the
tube's material, its thickness, and the intended use of active
cannula 102.
[0048] As in the case of outer flexible tube 110, middle flexible
tube 115 may be made of a shape memory alloy, such as nitinol,
although other materials may be used provided that they are
suitable for surgical use and have a flexibility that can be
predetermined by, for example, specifying a certain thickness for
the tube. Further, middle flexible tube 115 may or may not be made
of the same material as outer flexible tube 110, depending on the
intended shape, thickness, and overall flexibility of active
cannula 102.
[0049] FIG. 2C illustrates an exemplary inner flexible tube 120.
Inner flexible tube 120 may have an inner tube straight section
220, an inner tube curved section 222, and an inner tube transition
point 221 defining the boundary between inner tube straight section
220 and inner tube curved section 222. Inner flexible tube 120 may
have an inner diameter that is sufficiently wide to serve as a
cannula for passing fluids, etc. Further, the inner diameter may be
sufficiently wide to enable a cable, such as a wire, needle,
elastic push-rod, or fiberoptic cable, to be carried to end
effector 125. The thickness of inner flexible tube 120 may be a
function of the tube's desired flexibility, which is described
herein further below. Accordingly, the thickness of inner flexible
tube 120 may be tailored to provide a specified flexibility. The
illustrated curvature of inner flexible tube 120 is exemplary, and
many different curvatures are possible, given the tube's material,
its thickness, and the intended use of active cannula 102.
[0050] As in the case of outer flexible tube 110, inner flexible
tube 120 may be made of a shape memory alloy, such as nitinol,
although other materials may be used provided that they are
suitable for surgical use and have a flexibility that can be
predetermined by, for example, specifying a certain thickness for
the tube. Further, inner flexible tube 120 may or may not be made
of the same material as outer flexible tube 110 and middle flexible
tube 115.
[0051] End effector 125 may be one of many devices suitable for the
intended surgical intervention. For example, end effector 125 may
be a thermal ablation probe, a fiber-optic camera, a tip for
injecting radioactive seeds, a needle for performing a biopsy, and
the like. Further, end effector 125 may be used for acquiring
tissue or fluid samples for external analysis. Still further, end
effector 125 may be a bio-sensor to be deployed within a site of
interest. Such bio-sensors may include stereotactic positioners
(e.g., magnetic trackers), molecular sensors, electrical impedance
sensors, contactless mechanical impedance sensors, optical
luminescent sensors, and the like. It will be readily apparent to
one skilled in the art that end effector 125 may take many forms
and perform many different functions, all of which are within the
scope of the invention.
[0052] FIG. 2D illustrates active cannula 102, including each of
the tubes illustrated in FIGS. 2A-D. Inner flexible tube 120 is
illustrated as inserted into middle flexible tube 115, and the
combination of inner flexible tube 120 and middle flexible tube 115
are inserted within outer flexible tube 110.
[0053] FIG. 3 illustrates active cannula 102, including inner
flexible tube 120, middle flexible tube 115, and outer flexible
tube 110. As illustrated, each flexible tube has two degrees of
freedom: one around an axial rotational axis, and another along a
linear translational axis. For example, outer flexible tube 110 has
an outer rotational degree of freedom 305 and an outer translation
degree of freedom 310. Outer rotational degree of freedom 305 and
outer translational degree of freedom 310 apply to outer flexible
tube 110 independently of the other tubes. Middle flexible tube 115
has a middle rotational degree of freedom 315 and a middle
translation degree of freedom 320, both of which apply only to
middle flexible tube 115 independently of the other tubes. Inner
flexible tube 120 has an inner rotational degree of freedom 325 and
an inner translation degree of freedom 330, both of which apply to
inner flexible tube 120 independently of the other tubes.
[0054] Referring again to FIG. 3, active cannula 102 has a
plurality of overlap transition points T.sub.1-T.sub.5. Each
overlap transition point T.sub.1-T.sub.5 defines a boundary of a
region in which the each of outer flexible tube 110, middle
flexible tube 115, and inner flexible tube 120 (or some subset of
the three) have a substantially constant degree of curvature, or
lack of curvature. For example, the region between overlap
transition points T.sub.1 and T.sub.2 includes outer tube curved
section 212, middle tube straight section 215, and inner tube
straight section 220. Overlap transition point T.sub.2 is
coincident with middle tube transition point 216. Accordingly, the
region between T.sub.2 and T.sub.3 includes outer tube curved
section 212, middle tube curved section 217, and inner tube
straight section 220.
[0055] Each region bounded by at least one of overlap transition
points T.sub.1-T.sub.5 has a curvature that is a function of the
curvatures and flexibilities of each of outer flexible tube 110,
middle flexible tube 115, and outer flexible tube 120, as well as
the resistance of the surrounding tissue medium. One will note that
some regions have only middle flexible tube 115 and inner flexible
tube 120. In this case, the curvature of that region is a function
of the curvature of those two tubes within the region. In the
simplest case, the curvature of the region from T.sub.5 to end
effector 125 is a function of the curvature of inner flexible tube
120 and the resistance of the surrounding tissue medium.
[0056] FIG. 4A illustrates a set of two-axis actuators according to
the present invention. The two-axis actuators include outer drive
module 130, which is coupled to outer flexible tube 110; middle
drive module 135, which is coupled to middle flexible tube 115; and
inner drive module 140, which is coupled to inner flexible tube
120. Each of these drive modules independently drive their
respective flexible tube. For example, outer drive module 130
drives outer flexible tube 110 about outer rotational degree of
freedom 305 and along outer translational degree of freedom 310.
Middle drive module 135 drives middle flexible tube 115 about
middle rotational degree of freedom 315 and along middle
translational degree of freedom 320. And inner drive module 140
drives inner flexible tube 120 about inner rotational degree of
freedom 325 and inner translational degree of freedom 330.
[0057] FIG. 4B illustrates an exemplary two-axis actuator 405
according to the present invention. Two-axis actuator 405 may be
used for any of outer drive module 130, middle drive module 135,
and inner drive module 140. Two-axis actuator 405 includes a lead
screw 410, which may be rigidly attached to a flexible tube (outer
flexible tube 110 is illustrated as an example); a nut 415 that is
threaded onto lead screw 410; and a linear translation motor 435,
which is coupled to nut 415 via translation gear 425. Two-axis
actuator 405 further includes a belt drive 440, which is coupled to
lead screw 410 via sprocket 437. Belt drive 440 is also coupled to
rotation motor 450 via rotation gear 445. Two axis actuator 405 may
also include translational and rotational encoders (not shown) that
respectively provide linear translation position and angular
orientation signals to control computer 145.
[0058] Two-axis actuator 405 may operate as follows. In the case of
linear translation, linear translation motor 430 receives commands
from control computer 145 to translate its flexible tube according
to a particular translation distance. In response, linear
translation motor 430 rotates translation gear 425, which engages
nut 415. The subsequent rotation of nut 425 engages lead screw 410,
which translates the flexible tube.
[0059] In the case of rotation, rotation motor 450 receives
commands from control computer 145 to rotate according to a
particular rotation angle. In response, rotation motor 450 rotates
rotation gear 445, which engages belt drive 440. Belt drive 440
engages sprocket 437, which in turn rotates lead screw 410. Note,
this rotation of lead screw 410 causes a translation of lead screw
410 due to the presence of nut 415. Accordingly, to prevent a
parasitic translation, linear translation motor 430 compensates by
rotating nut 415 in the opposite direction. As such, pure rotation
of the flexible tube may require coordinated motion by rotation
motor 450 and linear translation motor 430.
[0060] As illustrated in FIG. 4B, lead screw 410 may be hollow. In
this case, if two-axis actuator 405 serves as outer drive module
130, then outer flexible tube 110 is coupled to lead screw 410, and
middle flexible tube 115 and inner flexible tube 120 may
independently translate and rotate within the hollow portion of
lead screw 410. In this way, outer flexible tube 110, middle
flexible tube 115, and inner flexible tube 120 may be translated
and rotated independently.
[0061] FIG. 5 illustrates a set of manual two-axis actuators
505a-c. Here, manual two-axis actuator 505a may drive outer
flexible tube 110 in place of outer drive module 130; manual
two-axis actuator 505b may drive middle flexible tube 115 in place
of middle drive module 135; and manual two axis actuator 505c may
drive inner flexible tube 120 in place of inner drive module 140.
Each of manual two axis actuators 505a-c may include translational
and rotational encoders, which provide linear position and angular
orientation signals to control computer 145.
[0062] Variations to the two-axis drive modules are possible. For
example, two-axis actuator 405 may include manual controls, such as
knobs, which respectively override linear translation motor 430 and
rotational motor 450. Further, system 100 may include a combination
of motor-driven and manual actuators. Further, two-axis actuator
405 is exemplary. As such, there may be other ways of achieving
linear translation and rotation of each of the flexible tubes apart
from the ways shown here. One skilled in the art will readily
appreciate that many such variations are possible and within the
scope of the invention.
[0063] FIG. 6 illustrates an exemplary process 600 for controlling
an active cannula associated with the present invention. All or
part of process 600 may be performed by the software stored on
memory 152 and executed on host computer 150 and/or control
computer 145 and/or imager processor 165. Process 600 may be
divided into two sub-processes: path planning (steps 605-625) and
path plan execution (steps 630-655).
[0064] In step 605, medical imaging system 160 acquires an image of
patient's anatomy 170. Medical imaging system 160 maybe configured
to have a field of view than encompasses entry point 175 and the
surgical site 180. Depending on its imaging modality (e.g. MRI,
ultrasound, etc.), medical imaging system 160 may acquire a 3-D
image of patient's anatomy, whereby each pixel or voxel of the
image is registered to an image coordinate frame. Imager processor
165 may provide the image, as well as image registration
information, to host computer 150 over imaging network connection
146b.
[0065] In step 610, the physician determines a desired path from
entry point 175 to surgical site 180. In doing so, the physician
may identify a path through which active cannula 102 will travel,
along with an error boundary around the path. Depending on the
location of surgical site 180, and the presence of intervening
tissue or organs, the path may involve a complex path having
variable error boundaries.
[0066] The physician may use user interface 155 to define the path
and its error boundaries. In doing so, the physician may use a
cursor to tag points within the registered image acquired in step
605. The software identifies the location of these selected points
in the registered image and stores these locations in memory
152.
[0067] In step 615, the software computes a final configuration of
active cannula 102 that will achieve the path selected in step 610.
In doing so, the software may determine the translational position
and rotational orientation of each of outer flexible tube 110,
middle flexible tube 115, and inner flexible tube 120, that will
make active cannula 102 conform to the path.
[0068] In computing a final configuration that conforms to the
path, the software divides active cannula 102 into a set of regions
defined by overlap transition points T.sub.1-T.sub.5. In doing so,
the software may select an initial set of translational positions
and rotational orientations for each of outer flexible tube 110,
middle flexible tube 115. The locations of overlap transition
points T.sub.1-T.sub.5 depends on the overlap of the three flexible
tubes. Then for each region bounded by overlap transition points
T.sub.1-T.sub.5, the software computes the instantaneous
equilibrium curvature (in x and y components) in that region
according to the following relation:
.kappa. x = i = 1 n E i I i cos ( .theta. i - .phi. ) .kappa. i i =
1 n E i I i ##EQU00001## and ##EQU00001.2## .kappa. y = i = 1 n E i
I i sin ( .theta. i - .phi. ) .kappa. i i = 1 n E i I i
##EQU00001.3##
where n is the number of flexible tubes (n31 3 in this example);
.kappa..sub.i is the instantaneous curvature of the i.sub.th
flexible tube in that region; E.sub.i is the Modulus of Elasticity
(Young's Modulus) of the material in the i.sub.th flexible tube;
I.sub.i is the cross sectional moment of inertia of the i.sub.th
flexible tube; .theta..sub.i is the angular orientation of the
i.sub.th flexible tube at the closest overlap transition point T in
the direction toward the actuators; and .phi. is the equilibrium
angle of combined flexible tubes given their individual angular
orientations, wherein .phi. is determined at the base of the
region. In other words, for example, for a region bounded by
overlap transition points T.sub.3 and T.sub.4, .phi. is pertains to
the equilibrium angle at T.sub.3.
[0069] Of these terms, .kappa..sub.i, E.sub.i, and I.sub.i are
known. The remaining terms are solved for by (1) computing the
torsional energy in the straight sections between the actuators and
the first transition point and the bending energy (as a function of
flexible tube orientations) stored in active cannula, and (2)
solving for the shape that provides the minimum energy. In doing
so, the software computes the torsional energy stored in straight
sections 210, 215, and 220 of outer flexible tube 110, middle
flexible tube 115, and inner flexible tube 120, respectively; and
the software computes the bending energy stored in curved sections
212, 217, and 222 of outer flexible tube 110, middle flexible tube
115, and inner flexible tube 120, respectively. The software does
this by computing the combined stored energy according to the
following relation:
E ( q ) = i = 1 n G i J i L i ( .alpha. i - .theta. i , 1 ) 2 + j =
1 m i = 1 n E i I i l i 2 ( ( .kappa. x - .kappa. i cos ( .theta. i
, j - .phi. j ) ) 2 + ( .kappa. i sin ( .theta. i , j - .phi. j ) )
2 ) ##EQU00002##
where .alpha..sub.i is the angle input at inner drive module 140,
middle drive module 135, and outer drive module 130;
.theta..sub.i,j is the angle of the i.sub.th flexible tube at the
j.sub.th transition point T.sub.j; .phi..sub.1, .phi..sub.2, . . .
.phi..sub.m are the equilibrium planes of each of the m regions of
overlap between overlap transition points T; and
q=(.theta..sub.1,1, .theta..sub.1,2, . . . .theta..sub.1,n,
.phi..sub.1, .phi..sub.2, . . . , .phi..sub.m). Solving for the
minimum value of E(q) yields the rotational orientations
.theta..sub.1,1, .theta..sub.1,2, . . . , .theta..sub.1,n at
T.sub.1, and the equilibrium planes .phi..sub.1, .phi..sub.2, . . .
, .phi..sub.m of each region of overlap between transition points
T. These values can also be used in the equations for .kappa..sub.x
and .kappa..sub.y above to compute the curvatures in each overlap
region between transition points T of active cannula 102.
[0070] FIG. 7 illustrates a kinematic frame for controlling a
flexible tube. As illustrated, .phi. refers to the equilibrium
angle of flexible tube 710 at an overlap transition point T.sub.i,
and .alpha. refers to the input rotation angle imparted by the
rotational motor of two-axis actuator 405.
[0071] Further to step 615, the software may select different tubes
from among an inventory of tubes for outer flexible tube 110,
middle flexible tube 115, and inner flexible tube 120. In this
case, a plurality of each flexible tube types may be available, and
their characteristics (length of straight section, length of curved
section, radius of curvature of the curved section, flexibility,
etc.) may be stored in memory 152. As such, the software may repeat
the above computation within step 610 described above, wherein each
iteration uses a different available tube. In this manner, the
software can determine two things: first, whether the path
determined by the physician can be replicated by active cannula
102; and second, what combination of tubes will achieve that path.
Further, the above relations are not limited to three flexible
tubes. Accordingly, the software may select varying combinations of
tubes, including the number of flexible tubes to be used, in order
to achieve the path determined by the physician. One skilled in the
art will understand how to implement the above equations for more
than three flexible tubes.
[0072] In step 620, the software computes a plurality of
configurations for active cannula 102 that will enable active
cannula to gradually achieve the final configuration computed in
step 615, while not having the active cannula stray beyond the path
and error boundaries determined by the physician. In doing so, the
software may compute a series of intermediate configurations, and
compute a set of linear translations and rotations that will
achieve each intermediate configuration. The software may
iteratively perform computations substantially similar to that
performed in step 615 above, with the resulting configuration for
each computed intermediate configuration being the initial
configuration for the next computed intermediate configuration.
[0073] Further to step 620, the software may compute a sequence of
rotation commands for rotation motors 450 and linear translation
commands for linear translation motors 430, of each outer drive
module 130, the middle drive module 135, and the inner drive module
140, in order to achieve each intermediate configuration in
sequence.
[0074] In step 625, the software registers the final and
intermediate configurations for active cannula, as respectively
computed in steps 615 and 620, in the coordinate frame of medical
imaging system 160. In doing so, the software may retrieve the
registered image acquired in step 605, in which the physician had
designated a path in step 610, and register the final and
intermediate configurations of active cannula 102. The result of
this may be a set of curves, one per intermediate configuration and
one for the final configuration, wherein each set of curves
corresponds to the regions of active cannula 102 between a overlap
transition points T.sub.1-T.sub.5. The software may do this by
starting at an origin point for the active cannula (registered in
image space), proceeding through entry point 175, and concluding at
surgical site 180 (or at end effector 125 for active cannula 102 in
an intermediate configuration). The software stores these sets of
curves in memory 152.
[0075] This completes the exemplary path planning subprocess of
process 600. The path planning sub-process may be performed in the
operating room, immediately before performing surgery.
Alternatively, the path planning sub-process may be done
pre-operatively and in a different setting than the operating room.
In the latter case, the image acquired in step 605 may be out of
date, because the patient will have moved between the path planning
sub-process and the execution sub-process. In this case, a new
registered image will have to be acquired by medical imaging system
160 as a precursor to the execution sub-process, and the
newly-acquired image will have to be registered to the earlier
registered image having the registered configurations (curves) of
active cannula 102 computed in step 625. Further information
regarding robotic path planning can be found in Planning
Algorithms, Steven M. LaValle, Cambridge University Press (2006),
(ISBN-10: 0521862051| ISBN-13: 9780521862059), which is hereby
incorporated by reference as if fully disclosed herein.
[0076] At the outset of the execution sub-process, the patient is
prepared for surgery and patient's anatomy 170 is placed within the
field of view of medical imaging system 160, as illustrated in FIG.
1. Active cannula 102 is placed in the vicinity of entry point 175,
and outer drive module 130, middle drive module 135, and inner
drive module 140 are connected to active cannula 102. Control
computer 145 is connected to the three drive modules 130, 135, and
140, and communications is established between control computer 145
and host computer 150 over control network connection 146a.
[0077] In step 630, the first step of the execution sub-process,
the physician (via user interface 155) issues a command to the
software to move active cannula 102 to the first intermediate
configuration computed in step 630 (in the path planning
sub-process). In doing so, the software, which may be running on
host computer 150 and/or control computer 145, issues appropriate
commands to the translational motors 430 and the rotational motors
450 of each of outer drive module 130, middle drive module 135, and
inner drive module 140, to achieve the first intermediate
configuration computed in step 620.
[0078] In step 635, medical imaging system 160 acquires an image of
active cannula 102 within patient's anatomy 170. In doing so,
imager processor 165 may segment and register active cannula 102 in
the image coordinate frame. Imager processor 165 may employ one or
more segmentation algorithms that are known to the art. Imager
processor 165 may transmit the registration information and the
image to host computer 150 over imaging network connection 136b.
The software may receive the registration information and the image
of active cannula 102 within patient's anatomy 107 and present the
information and image to the physician via user interface 155.
[0079] In step 640, the software compares the registered image of
cannula 102 with the intermediate configuration computed in step
620. In doing so, the software may employ one or more of a number
of image processing algorithms for comparing the two images.
Further, the software may compare the coordinates of the segmented
and registered active cannula 102 with the computed coordinates of
the given intermediate configuration and compute a path error, or
differential displacement, based on this comparison.
[0080] In step 645, the software determines if there is a
discrepancy between the segmented and registered active cannula 102
with the given intermediate configuration. If there is no
discrepancy, process 600 proceeds through the "NO" branch from step
645 to step 655.
[0081] In step 655, the software determines if the given
intermediate configuration is the final configuration computed in
step 615. If it is, process 600 may proceed through the "YES"
branch of step 655 to completion. If it is not the final
configuration, then process 600 may proceed through the "NO" branch
of step 655 to repeat steps 630-645 with the next intermediate
configuration (or the final configuration).
[0082] Returning to step 645, if there is a discrepancy between the
segmented and registered active cannula 102 with the given
intermediate configuration, process 600 may proceed through the
"YES" branch of step 645 to step 650.
[0083] In step 650, the software computes the force and torque
exerted on active cannula 102 as it was pushed through patient's
anatomy 170 in step 630. The software may compute the force and the
torque according to the following relations:
[ f x f y f z .tau. x .tau. y .tau. z ] = [ K ] [ disp x disp y
disp z rot x rot y rot z ] ##EQU00003##
where f.sub.x,y,z are components of the force imparted by the
tissue medium on active cannula 102 at a given region between two
overlap transition points T.sub.i and T.sub.i+1i; .tau..sub.x,y,z
are the torques imparted on active cannula 102 by the tissue medium
on active cannula 102 at the same region; disp.sub.x,y,z are
translational components of the differential displacement of active
cannula 102 computed in step 640; rot.sub.x,y,z are the rotational
components of the differential displacement of active cannula 102
computed in step 640; and K is a compliance matrix, which is a
6.times.6 matrix corresponding to the force and torque compliance
of active cannula 102 for the given region between two overlap
transition points T.sub.i and T.sub.i+1.
[0084] Compliance matrix K may be predetermined in a calibration
procedure in which active cannula 102 is translated and rotated in
one or more phantoms having known resistance properties. In
addition, if compliance matrix K is known, then active cannula 102
may be used as a force sensor. In this case, a physician may plan a
path for active cannula (using all or part of exemplary process
600) so that end effector 125 may come in contact with a tissue
region of interest. Once end effector 125 comes in contact with the
tissue region of interest, the values for f.sub.x,y,z and
.tau..sub.x,y,z computed in step 650 may respectively correspond to
the force and torque imparted on end effector 125 by the tissue
region of interest. Accordingly, active cannula 102 may be used as
a force sensor.
[0085] FIG. 8 illustrates how strain relates to the side lengths of
a flexible tube, which may be any of outer flexible tube 110,
middle flexible tube 115, and inner flexible tube 120. The
software, in computing the final and intermediate configurations in
steps 615 and 620, may determine the maximum degree of curvature,
or minimum radius of curvature, beyond which a given flexible tube
will suffer plastic deformation. Plastic deformation refers to the
degree of bending of a shape memory material such that the material
will no longer return to its original shape. This may correspond to
a limit of permissible curvature of a flexible tube. The software
may compute the maximum degree of curvature according to the
following relation:
.kappa. = 2 d ( 1 + ) ##EQU00004##
where d is the diameter of the flexible tube, and .epsilon. is the
maximum recoverable strain for the flexible tube's material. For
nitinol, .epsilon. may range from 0.08 to 0.1. As can be inferred
from the above relation, the thinner the flexible tube, the greater
the maximum degree of curvature (or the lesser the minimum radius
of curvature). Accordingly, depending on the path determined by the
physician in step 610, a thinner flexible tube may be desired. The
software may assist the physician in selecting a preferred
thickness of flexible tube depending on the path determined in step
610.
[0086] Variations to active cannula 102, system 100, and process
600, are possible and within the scope of the invention. For
example, some or all of the flexible tubes in active cannula 102
may have substantially the same degree of flexibility, or they may
each have different degrees of flexibility. If all of the flexible
tubes have a similar flexibility, it may make active cannula 102
more agile and easier to guide through complex paths.
Alternatively, outer flexible tube 110 may be stiffer than middle
flexible tube 115, which may be in turn stiffer than inner flexible
tube 120. In the latter case, active cannula 102 may be less agile
than in the former case (in which all the flexible tubes have the
same flexibility). However, in the latter case, the path of active
cannula 102 may be easier to compute, and it may better enable
manual operation, for example, by using manual two-axis actuators
505 illustrated in FIG. 5.
[0087] In another variation, any of the flexible tubes may have
non-circular inner and/or outer shapes. Such variations to a
flexible tube's cross section may provide differing flexibility as
a function of bend angle. Further, a flexible tube may have
different shaped regions along its length, whereby each region may
have a different cross sectional shape.
[0088] Any of the flexible tubes within active cannula 102 may have
only a curved portion or a straight portion. Further, any of the
flexible tubes may have multiple segments, each with a different
degree of curvature (including no curvature). This may allow active
cannula 102 to take more complex shapes. For example, any of the
flexible tubes may have sequences of three-dimensional curves and
straight regions. Also, any of the flexible tubes may have a
segment having an complex shape, such as a helical shape, an
elliptical shape, a parabolic shape, a variable curvature in three
dimensions, and the like. In any of these cases, multiple
transition points (like inner tube transition point 221, middle
transition point 216, and outer tube transition point 211) may be
defined that mark changes in radius of curvature of the particular
flexible tube. Accordingly, discrete gradations of curvature may be
segregated for the purposes of defining overlap regions, as part of
computing cannula final and intermediate configurations in steps
615 and 620.
[0089] In another variation, one or more of the flexible tubes may
be designed to have a variable stiffness according to the direction
in which the flexible tube is bent. For example, one or more of the
flexible tubes may have scores or grooves on the inner or outer
surface of the flexible tube.
[0090] In another variation, one or more of the flexible tubes may
include fiducials, which may be embedded within the tube material,
and which may be designed to be visible to medical imaging system
160. For example, if medical imaging system 160 is an optical
camera, embedded fiducials may take the form of colored stripes or
bands of light and dark color. Further, if medical imaging system
is a C-arm fluoroscope, embedded fiducials may include wire
structures implanted within the tube material. One skilled in the
art will readily appreciate that many such variations are possible
and within the scope of the invention.
[0091] If nitinol is used for any of the flexible tubes described
above, then system 100 may include one or more heater elements,
which may run along one or more of flexible tubes 110, 115, and
120. According to this variation, heat can be applied to change the
shape of a given flexible tube. One skilled in the art will
understand how to integrate a heater element into active cannula
102 and system 100 and that such a variation is within the scope of
the invention.
[0092] In addition to lung and throat surgery, as mentioned above,
the present invention may be used in other surgical procedures, in
which the dexterity afforded by active cannula 102 and system 100
may be advantageous. Such surgical procedures include
Radiofrequency Ablation. In Radiofrequency Ablation, an electrode
is placed at a surgical site, and then a painless radiofrequency
energy is transmitted to heat the tissue surrounding the electrode.
This procedure may be used to kill cells as part of a treatment for
tumors of the liver, kidney, and lung. Active cannula 102 and
system 100 may be employed to deploy the electrode.
[0093] Another possible surgical application involves surgical
interventions on the posterior side of the retina. One such
surgical intervention may include cannulation of the retina to
treat clotting, which is one of the leading causes of
blindness.
[0094] Another possible surgical application involves transgastric
surgery, in which tools enter the stomach via the mouth, then exit
the stomach into the abdominal cavity. The dexterity of active
cannula 102, and its ability to be guided through free space as
well as through tissue, may enable transgastric surgery.
[0095] In another variation, system 100 may include a second active
cannula 102, which includes a second set of inner, middle, and
outer drive modules connected to control computer 145. In this
variation, the two active cannulas can be used as a parallel robot
(a "Stuart Platform" is an exemplary type of parallel robot, but
many variants are known in the art) whereby the tips of the inner
flexible tubes of the two active cannulas are coupled to a single
end effector 125. Doing so may enable the system to control the
position and orientation of the end effector as well as control the
stiffness of the position and orientation. In another application
of the variation to system 100 having two active cannulas, the two
active cannulas may be deployed within patient's anatomy 170 and
used as retractors for holding soft tissue away from and exposing a
surgical site.
[0096] Although the above description pertains to a surgical
application of the present invention, it will be readily apparent
to one skilled in the art that the present invention may be used in
other applications that require guiding a device through a complex
path that involves free space. Other applications may include
manufacturing and micro-assembly, remote structural inspection,
defusing ordinance, search and rescue within collapsed structures,
and the like.
[0097] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention
without departing from the spirit or scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *